- Why bicontinuity is the right condition for topological equivalence (homeomorphism): if continuity of the inverse isn’t required, then a circle could be equivalent to a line (.99999 and 0 would be neighbours) — Minute 8 or so.
- Geometric construction (no complex numbers) of the circle group.
- Pappos’ theorem. (Minute 31)
- Pascal’s theorem.
- Desargues’ theorem.
Hat tip to +Ozymandias Haynes.